Originally Posted by
exbayern
How can TSA be screening you when you fly TO the US?
That would be CATSA, not TSA, at the security checkpoint in Canada.
You are right it is CATSA that does the screening in Canada, but I was told that the flag for secondary comes as a result of the TSA secure flight info that is sent when flying to the US. So ultimately it is the TSA that generates the screening request.